The present invention relates to antenna arrays for radar systems, and, more particularly, to electronically steerable radar arrays adaptable for use in aircraft surveillance radar systems.
Antenna arrays for aircraft surveillance radar systems require high gain, wide-band operation and low aerodynamic loading with full 360 degree azimuth scanning capability. Such radar systems can be mounted on aircraft which operate in flight in an Airborne Early Warning (AEW) system.
The designs of prior AEW type antenna arrays have encumbered this type of antenna arrays with general inflexibility, excessive aerodynamic loading, disadvantages of mechanical scanning operation, and/or limited electronic scanning capability.
In prior antenna arrays having electronic scanning, large apertures placed parallel to the air stream have employed high-gain radiating elements and have thus provided high antenna gain with aerodynamic loading limited through control of the antenna frontal area. Dorsal fins, billboards attached to the sides of aircraft, triad phased and other structures have housed AEW type antenna arrays, but none of these approaches has been entirely successful in meeting gain, aerodynamic, and electronic scanning objectives together.
A basic problem results from the fact that placement of large apertures parallel to the air stream provides required high antenna gain but simultaneously makes it difficult to produce full-azimuth electronic scanning. Electronic steering systems in most prior art systems cannot provide beam steering sufficiently forward or aft to achieve 360 degree scanning primarily because of the side-looking location of radiating elements in the arrays placed parallel to the air stream.
In a more recent development, as disclosed in U.S. patent application Ser. No. 08/489,569, entitled INTEGRATED FULL COVERAGE ANTENNA MODULE, filed on Jun. 12, 1995 by Timothy G. Waterman et al, and assigned to the current assignee, an antenna array is provided with end fire arrays positioned on and under opposed side-looking arrays. This module achieves full scanning, but it employs high-gain, end-fired radiating elements with little or no elevation scanning capability, has otherwise generally limited scanning flexibility, and carries other disadvantages of the prior conventional side-looking antenna arrays.
A need has thus existed for a better antenna array adaptable for AEW surveillance applications with more flexible electronic scanning, reduced aerodynamic loading, and generally more effective surveillance.